Crystallinity of isothermally and nonisothermally crystallized poly(ether ether ketone) composites

PEEK/carbon fiber composites were prepared by a modified diaphragm forming machine under vacuum. The study of the degree of crystallinity versus the differential scanning calorimetry (DSC) heating rate indicated that 50 degrees C/min was an optimal heating rate to suppress the reorganization of the specimens crystallized between 315 degrees C and 255 degrees C and to avoid superheating the specimens. A high volume of fibers constrained the spherulitic growth by an impingement mechanism, which depressed the crystallization rate and reduced the crystallinity. Thus the crystallization was still in process even after 240 min annealing at 300 degrees C. The effect of the cooling rate on the degree of crystallinity was simulated and investigated in DSC at a heating rate of 50 degrees C/min. The results indicated that the cooling rates ranging from 1 degrees C/min to 100 degrees C/min could be divided into five regions that were associated with a high volume of fiber and the crystallization regime. A Time-Temperature-Transformation diagram superposed on the Continuous-Cooling-Transformation curves allows us to predict the amount of crystallization in different regimes. The data points for the DSC method deviated from the prediction at the cooling rates above 60 degrees C/min because of the recrystallization during DSC heating scans.